A network processor generally controls the flow of data between a physical transmission medium, such as a physical layer portion of, e.g., an asynchronous transfer mode (ATM) network or synchronous optical network (SONET), and a switch fabric in a router or other type of packet switch. Such routers and switches generally include multiple network processors, e.g., arranged in the form of an array of line or port cards with one or more of the processors associated with each of the cards.
An important function of a network processor involves the scheduling of packets or other data blocks for transmission, e.g., for transmission to the switch fabric from the network or vice versa. A network processor typically includes a scheduler for implementing this function. One way that such a scheduler may be implemented involves the use of demand-based time slot tables, also referred to as dynamic time slot tables. In these cases, a significant problem that can arise relates to the manner in which the scheduler deals with transmission request collisions, that is, simultaneous requests for transmission in the same time slot. Typically, only a single block of data can be transmitted in a given time slot. When multiple data blocks request transmission in the same time slot, only one of the blocks can be transmitted, and the other blocks must be delayed or dropped. It should be noted that this problem is specific to demand-based time slot tables, and is generally not an issue for static time slot tables which can be configured to avoid collisions altogether.
The above-noted problem with demand-based time slot tables makes it difficult to maintain a desired traffic shaping for the transmitted data blocks in the corresponding network processor. This in turn complicates the provision of desired service levels, e.g., specified quality of service (QoS) or class of service (CoS) levels, for particular network connections supported by the network processor.
Another problem with conventional network processors is that such processors fail to provide acceptable implementations of programmable service level. For example, such processors generally use fixed, custom logic design to implement a particular CoS scheduling algorithm. Although attempts have been make to make this approach more flexible by allowing configurable weights for different classes of service, the particular algorithm remains fixed and therefore not reconfigurable under software control. As a result, these conventional processors are generally suitable for use only in the specific applications that require the particular CoS scheduling algorithm for which the processors were designed.
A need therefore exists for improved scheduling techniques for use in a network processor, so as to facilitate the provision of QoS, CoS or other desired service levels for corresponding network connections.